Nixpkgs: KDE will not automatically update it's start menu

[Chiiruno]

Issue description

KDE does not automatically run kbuildsycoca5, thus leading to broken links to software that NixOS is in fact correctly linking in /run/current-system/sw/share/applications

Steps to reproduce

Install KDE Plasma 5.
Use it for a little while.
Notice sometimes stuff like the steam desktop file will not update, or after a nixos-rebuild switch the start menu will not display new packages, either until a logout, a restart, or running kbuildsycoca5 in the terminal.

Technical details

• system: "x86_64-linux"
• host os: Linux 4.14.41, NixOS, 18.03.132405.ee80654b526 (Impala)
• multi-user?: yes
• sandbox: yes
• version: nix-env (Nix) 2.0.1
• channels(root): "nixos-18.03, nixos-unstable, nixpkgs"
• nixpkgs: /nix/var/nix/profiles/per-user/root/channels/nixos/nixpkgs

[Anton-Latukha]

Singleton of #20776.

Informing @ttuegel .

[Chiiruno]

A hook for executing kbuildsycoca5 when upgrading your system would be nice.

[Chiiruno]

Whoops.

[ttuegel]

A hook for executing kbuildsycoca5 when upgrading your system would be nice.

That would be nice, but AFAIK nixos-rebuild does not have hooks. One workaround for individual users would be to make a shell alias, but that's not something we could realistically deploy for everyone using NixOS.

[bjornfor]

The activation script mechanism could be used, right?

[ttuegel]

The activation script mechanism could be used, right?

Can activation scripts run as an arbitrary user?

[bjornfor]

I think it runs as root, so we could use su/sudo to arbitrary user.

[Chiiruno]

Perhaps getting a list of users and then executing kbuildsycoca5 for each (valid) user?
Or is there a way to check which user executed the (sudo?) nixos-rebuild command?

[Chiiruno]

Also what about if a user su's into root or another user and then updates?
Perhaps getting a list and executing the command would be better, especially if on a multi-user system.

[schmittlauch]

Hm… This is still happening to me on 18.09: Nearly all start menu entries are broken and give a "Could not find the program" error message. Running kbuildsycoca manually doesn't fix the problem.

I'm managing most of my software using home-manager though, could that be an issue?

[tbenst]

Same problem for me as @schmittlauch

[pirboazo]

Same problem for me :-(
as
" @Vskilet
I'm on Nixos 18.09 and when I use kbuildsycoca5 nothing appears on command line ... And one day when I nix-env -ia something ... menu updated . "
workaround work :-)